1. Field of the Invention
An aspect of the present invention relates to at least one of a film formation method and a film formation apparatus.
2. Description of the Related Art
In recent years, a range of materials used for semiconductor devices is transitioning from an inorganic material to an organic material and an organic-inorganic hybrid material. In order to optimize the characteristic of or the manufacturing process for a semiconductor device, a high level of design of a material is being conducted by utilizing a difference between material characteristics of an organic material and an inorganic material.
For one of such organic materials, it is possible to provide a polyimide. A polyimide is excellent as an insulating property thereof, and hence, it is possible to be used for an insulting film in a semiconductor device.
For one example of a method for film-forming a polyimide film, a film formation method based on vapor deposition polymerization has been known that uses pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether that contains 4,4′-oxydianiline (ODA), as raw material monomers.
For example, a method for film-forming a polyimide film is disclosed in Japanese Patent No. 4283910, wherein PMDA and ODA monomers are vaporized by a vaporizer and supplied into a film formation unit to cause vapor deposition polarization on a substrate.
In order to obtain a good polyimide film by vapor deposition polymerization, it is necessary to supply certain amounts of vaporized PMDA and ODA into a film formation apparatus intermittently.
On the other hand, a trace amount of a metal component is usually mixed into PMDA as is a raw material at a time of manufacturing. This metal component influences an insulating property of an obtained polyimide film, and hence, is removed by material purification that uses acetic acid and/or acetic anhydride. However, a problem caused by an acetic acid component remaining in PMDA after this material purification is that it is difficult to supply a constant amount of PMDA into a film formation unit intermittently and stably.
Such an adverse effect caused by an impurity component at a time of supplying a raw material gas is not limited to that at a time of film formation of a polyimide film but is also a problem at a time when another organic film or an organic/inorganic composite film is film-formed.